Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $153.39   13.572%   $174.2081   $174.21   $174.20   $174.20  
  Purchase #2 $77.71   8.614%   $84.4039   $84.40   $84.40   $84.40  
  Purchase #3 $214.36   9.646%   $235.0372   $235.04   $235.05   $235.00  
  Purchase #4 $198.38   11.610%   $221.4119   $221.41   $221.40   $221.40  
  Purchase #5 $246.79   8.576%   $267.9547   $267.95   $267.95   $268.00  
  Purchase #6 $30.92   4.743%   $32.3865   $32.39   $32.40   $32.40  
  Purchase #7 $31.84   10.313%   $35.1237   $35.12   $35.10   $35.10  
  7 purchase totals = $953.39       $1,050.5260   $1,050.52   $1,050.50   $1,050.50